1. Field of the Invention
This invention relates to recording and reproducing apparatus providing a high efficiency coding adapted for digital video tape recorders and digital audio tape recorders.
2. Related Art Statement
Recently, the digital processing of pictures has been investigated. Particularly, in the field of high efficiency coding for compressing picture data, various systems have been suggested as the standard. In order to improve the efficiency of the digital transmission and recording, a high efficiency coding technique is used to code picture data with a smaller bit rate. As a standard for high efficiency coding systems, the CCITT (International Telegraph and Telephone Consultative Committee) has suggested the JPEG (Joint Photographic Experts Group) system for color still pictures and the MPEG (Moving Picture Experts Group) system for moving pictures in the television conference/television telephone standardizing recommendation draft H.261 (as described in detail in "High Efficiency Picture Coding System Integrated" in the "Electronics" No. 511, Oct. 15, 1990 published by Japan Economic Journal Company). All of these suggestions are systems based on the DCT (Discrete Cosine Transform).
FIG. 20 is an explanatory diagram for explaining the MPEG encoding system. In the diagram, the predictive directions of the coding are shown by arrows. FIG. 25 is an explanatory diagram showing the order of the picture data in the coding process, the arrangement on the media and the decoding process in the MPEG coding system.
In the MPEG coding system, a GOP (Group of Pictures) is formed by a predetermined number of frame 5 and contains at least one intra-picture coded picture I. The intra-picture coded picture I is picture data of one frame as coded by the DCT. The picture data of each predetermined frame from the intra-picture coded picture I is converted to a forward predictive coded picture P by the forward predictive coding. Then, the picture data of each frame between the intra-picture coded picture I and the forward predictively coded picture P are converted to a bidirectional predictively coded picture B by the bidirectional predictive coding using the forward and rearward predictive coding.
As shown in FIG. 25, the intra-picture coded picture I is coded first by only the information within the frame and contains no prediction in the time direction. Then, as shown in FIG. 25, a forward predictively coded image P is made and a bidirectional predictively coded picture B is coded after the intra-picture coded picture I or the forward predictively coded picture P. The forward predictively coded picture P and bidirectional predictively coded picture B utilize a correlation with the other picture data. Thus, because of the predicting method of the respective picture data, the coded picture B is recorded on the medium after the coded pictures I and P, and is returned to its original order when decoded.
The intra-picture coded picture I is coded by only the information within the frame and therefore can be decoded by only the coded data alone. On the other hand, the forward predictively coded picture P and bidirectional predictively coded picture B are coded by utilizing a correlation with the other picture data and can not be decoded with only the coded data.
The circuit shown in FIG. 26 is adopted for the predictive coder and decoder and is mentioned in the "TV Picture Multidimensional Signal Process" (written by Keihiko Fukinuki and published by Daily Industrial Newspaper Company, pages 221-). FIG. 28 is a waveform diagram for explaining the predictive coding of a television signal.
In the television signal, the correlation between pixels is high making the difference between pixels small. The predictive coding utilizes such statistical property and sight characteristic (difference sensitivity). In the simplest front value prediction, a predictive value xi' is determined by using the pixel xi-l or one pixel before the present pixel, xi. Usually, a linear prediction is made by representing the predictive value xi as xi'=a xi-l (a represents a prediction coefficient). If the difference (prediction error) from the true value is represented by .SIGMA.i, it can be calculated by the below mentioned formula (1) and then coded. FIG. 26 shows the case where the prediction coefficient a is 1: EQU .SIGMA.i=xi-xi'=xi-a xi-1 (1).
That is to say, in FIG. 28, the video signal from the camera 42 is converted by the A/D converter 43 to a digital signal which is input into the subtractor 44 and delaying circuit 45. The signal input into the delaying circuit 45 is delayed by one pixel and is then multiplied by the prediction coefficient a in the multiplier 46 and is given to the subtractor 44. In the subtractor 44, the output of the multiplier 46 is subtracted from the output of the A/D converter 43 to determine .SIGMA.i of the above mentioned formula (1). Then the output of the subtractor 44 is quantized by the non-linear quantizing circuit 47 and is output to the transmitting path 48. As the prediction error deviates in its distribution, as seen statistically, non-linear quantization is adopted in the coding.
On the other hand, the signal in the decoder from the transmitting path 48 is input into the typical value circuit 49. To reverse the compression characteristics of the non-linear quantizing circuit 47 of the coder, the typical value circuit 49 obtains the elongation characteristics by using the reverse of the function adopted in the non-linear quantizing circuit 47. The output of the typical value circuit 49 is given to the D/A converter and LPF (low pass filter) 51 through the adder 50, is converted to an analogue signal and is given to the delaying circuit 52. The output of the delaying circuit 52 is given to the adder 50 through the multiplier 53, which multiplies the signal by the prediction coefficient a. That is to say, the pixel xi of the above mentioned formula (1) is obtained by the loop of the adder 50, delaying circuit 52 and multiplier 53. The output of the D/A converter and LPF 51 is given to the monitor 54 and is displayed.
By the way, in order to prevent the quantizing strains of the non-linear quantizing circuit 47 from accumulating in the coder, the circuit shown in FIG. 27 is adopted. That is to say, the local decoder 55 comprising the typical value circuit 49, adder 50, delaying circuit 52 and multiplier 53 is adopted to make a signal given to the subtractor 44. Thus, the quantizing strains will not be accumulated.
Now, the above described MPEG coding system is considered to be applied to the DAT (digital audio tape recorder) or VTR (video tape recorder). FIG. 29 is a traced pattern diagram showing the recorded tracks in this case by the track pattern coordinate method. In the diagram, the hatched parts show the recording positions of the intra-picture coded pictures I.
In the MPEG coding system, the data of the coded pictures I shown by the hatches recorded on the recording medium. Then, the data of the bidirectional predictively coded pictures B and forward predictively coded pictures P are successively and repeatedly recorded. In FIG. 29, the first GOP is recorded until the midway of the fourth track. The next GOP is recorded from the midway of the fourth track to the last of the sixth track. The coded picture I of the picture at the top of the next GOP is recorded at the top of the seventh track.
In the MPEG coding system, the recording rate is regulated (typ. 1.2 Mbps) but the data length is variable. Therefore, as shown in FIG. 29, the position of the track in which the intra-picture coded picture I is recorded can not be specified and the data length of 1 GOP can not be also specified.
Even in this usual reproduction, the respective coded pictures I, B and P are successively reproduced, and therefore there is particularly no problem. However, at the time of special reproductions such as the quick feed reproduction, only a part of the recorded track will be reproduced, therefore the recording position of the intra-picture coded picture I on the recording medium will not be regularly arranged and the intra-picture coded picture I may not be reproduced. Even in cases where the other coded data is positively reproduced, this data will not be able to be decoded.
In a moving picture coding system, there is a method wherein only the intra-picture coding is adopted instead of the above described MPEG system. FIG. 30 is a block diagram showing a related art of a high efficiency coding recording and reproducing apparatus suggested in "An Experimental Study for a Home-Use Digital VTR" (IEEE Vol. 35. No. 3, August (1989).
In FIG. 30, a luminance signal Y of a video signal is sampled with a sampling clock, for example, at a frequency of 13.5 MH.sub.z and color difference signals Cr and Cb are sampled with a sampling clock, for example, at a frequency of 13.5/4 MH.sub.z. These signals Y, Cr and Cb are input into the memory 1 which converts the input interlaced signals to a frame structure and outputs horizontal and vertical direction 8.times.8 pixels as one block in a block unit to the bit rate reducing circuit 2.
FIG. 31 is a block diagram showing the bit rate reducing circuit 2.
In the DCT circuit 3 of the bit rate reducing circuit 2, a signal in which one block is formed of 8.times.8 pixels is input and converted to a frequency component by two-dimensional DCT (Discrete Cosine Transforming) processing of the 8.times.8 pixels. Thereby, the spatial correlative component can be reduced. That is to say, the output of the DCT circuit 3 is given to the adapted quantizing circuit 5 through the buffer memory 4 and is re-quantized by the adapted quantizing circuit 5 so that the redundancy of one block of the signal will be reduced. In this case, the data amount evaluating circuit 7 evaluates the amount of data the DCT circuit 3 and generates the coefficient based on the evaluated result. In the adapted quantizing circuit 5, the quantization is made on the basis of this coefficient.
The quantized data is then given to the variable length coding circuit 6 and is, for example, Haffman-coded on the basis of the result calculated from the statistical coded amount of the quantized output. Thereby, short bits are allotted to data having a high probability of appearing and long bits are allotted to data low in of probability appearing so that the transmitted amount will be further reduced. Thus, the data of 162 Mbps are compressed to 19 Mbps and is given to the coder 8 in FIG. 30.
In the coder 8, the parity for correcting errors is added to the data and output to the channel coder 10. In the coder 8, the variable length data of respective blocks are synchronized with synchronous signal.sub.s, converted to synchronous blocks of a fixed length, and output. In the channel coder 10, the output of the coder 8 and the voice signal from the voice processing circuit 9 are recorded and coded in response to the characteristics of the recording media, are given to the recording amplifier (R/A) 11 and are recorded in the medium 12. Thus, as shown in FIG. 32, the data of the respective blocks are converted to synchronous blocks of the same data length and are recorded.
At the time of reproduction, the signal reproduced from the recording medium 12 will be given to the detector 14 through the reproduction amplifier (H/A) 13. In the detector 14, the bit clock of the reproduced signal is detected, the recorded data are decoded, the TBC (Time Base Correction) process correcting the time axis or the like is made and then the data are output to the decoder 15, in which errors such as random errors and burst errors generated at the time of the recording and reproduction are corrected by correcting codes and given to the bit rate decoder 16. In the bit rate decoder 16, the variable length code from the decoder 15 is decoded, the reverse quantizing process and reverse DCT process are made and the original information is restored. In this case, a non-reversible compressing process will be made by the re-quantizing process and some strains will be generated. The data decoded by the bit rate decoder 16 are given to the memory 17, and are then output after being converted to be of the same format as the input. The voice signal from the detector 14 is voice-processed and is output by processing circuit 18.
Thus, the coded data will be recorded in a synchronous block unit of a fixed length at the time of the recording, with the picture and recording position corresponding to each other, with some special reproduction possible to some extent. However, a defect arises in that the compression efficiency is low.
Also, in the "Fixed Electronic Still Camera Rate Adapted Type DCT Coding System" suggested in the 1989 Telecommunication Society Spring Nation-wide General Meeting D-159 is disclosed an example that the recording is made by limiting the code amount in a unit recording time to a fixed range. FIG. 33 is a circuit diagram for explaining this suggestion.
A signal of one block of 8.times.8 pixels input through the input terminal 21 is DCT-processed by the DCT circuit 22 and is then given to the scan converting circuit 23. As shown in FIG. 29, the outputs (DCT conversion coefficients) of the DCT circuit 22 are arranged in the order from the low region components to the high region components in the horizontal and vertical directions. In the scan converting circuit 23, as the information concentrates in the low region components in the horizontal and vertical directions of the DCT conversion coefficients, the scan is made zigzag from the low region components toward the high region components in the horizontal and vertical directions to output the DCT conversion coefficients to the quantizing circuit 24. Note the number 0 in FIG. 34 shows a DC component (direct current component) and its value is an average value of all the conversion coefficients. The other parts are AC components.
On the other hand, a parameter .alpha. showing the information amount of the input image is input into the multiplier 26 through the input terminal 28. In the multiplier 26, the information of the basic quantizing coefficient preset for each frequency component of the DCT conversion coefficient is given from the Q table 27 and this information is multiplied by the parameter .alpha. and is output to the quantizing circuit 24 through the limiting circuit 25. In the quantizing circuit 24, the DCT conversion coefficient is quantized on the basis of the quantizing coefficient from the limiting circuit 25. That is to say, in the quantizing circuit 24, the quantization is corrected for each frequency component by the output of the limiting circuit 25 and the coding rate is controlled. Note that the minimum quantizing coefficient 25 is limited on the basis of the encoding efficiency and the data of the Q table 27.
A picture coding system has been suggested by the present applicant in the specification of Japanese Patent Application Laid Open No. 404811/1990. In that system the data appearing at the output terminal 30 in FIG. 33 are made to be of a fixed length. FIG. 35 is a block diagram for explaining this suggestion.
A signal of the macro-block shown in FIG. 36 is input into the input terminal 31. In case the sampling frequency is 4 f.sub.zc (f.sub.zc is a color sub-carrier frequency), the number of effective pixels of one frame picture will be approximately 768 horizontal pixels.times.488 vertical pixels. In the color difference signals Cr and Cb, the sampling rate in the horizontal direction is only 2 f.sub.sc. Therefore, while two luminance blocks of 8.times.8 pixels are sampled in the color difference signals Cr and Cb, respectively only one block of 8.times.8 pixels will be sampled. A macro-block is formed of these four blocks. The data of this macro block are input into the DCT circuit 33 through the buffer memory 32, are DCT-processed and are further quantized by the quantizing circuit 34 to obtain the same quantized output as the quantized output in FIG. 33. As shown in FIG. 37, at the top of each macro-block are added code amount data L showing the code amount of the macro-block.
This quantized output is divided by frequency, the low region component coded by the low region coding circuit 35 and the high region component coded by the high region coding circuit 36. The coded data from the low region and high region coding circuits 35 and 36 are given to the multiplexer (mentioned as MUX hereinafter) 39 respectively through the buffer memories 37 and 38 and are time-divided and multiplexed. FIG. 38 and FIG. 39 are explanatory diagrams for explaining the multiplex method. In FIG. 38, the low region component and high region component are successively arranged following the code amount data L. In FIG. 39, the low region component is arranged before the code amount data L and the high region component is arranged after the code amount data L.
The output of the MUX 39 is given to the packing circuit 40 and is provided with a macro-block address (MBA) and macro-block pointer (MBP) in a synchronous block unit. FIG. 40 is an explanatory diagram showing this state. The macro-block address shows the position on the picture in the macro-block, that is to say, the order within one frame or one field, for example, added following the synchronous signal. The macro-block pointer is added following this macro-block address and then the code amount data L and macro-block of FIG. 37 are arranged in the picture coding data sector. The picture coding data sector is sectioned by a unit of 54 bytes. As shown in FIG. 41, the macro-block is started or ended in the midway of the picture coding data sector. The macro-block pointer shows the byte position of the picture coding data sector from which the macro-block is started. Thus, the coded data fixed in the length within the frame are output from the packing circuit 40.
Also note that in the format of FIG. 40, two data P of the C1 series (61, 57) of the Read Solomon codes (R.S. codes) are added as error correcting codes. As error correcting codes in the magnetic recording system, the Read Solomon codes are often used as adopted in the "Error Correcting Apparatus" in the publication of Japanese Patent Application Laid Open No. 3224/1979, D-1 digital VTR, D-2 digital VTR and DAT. For example, in the D-1 standard, the codes of the C1 series (64, 60) and C2 series (32, 30) are adopted, in the D-2 standard, the codes of the C1 series (93, 85) and C2 series (68, 64) are adopted and, in the DAT, the codes of the C1 series (32, 28) and C2 series (32, 26) are adopted.
FIG. 42 is an explanatory diagram for explaining the D-1 standard. FIG. 43 is an explanatory diagram showing the recorded state of recording tracks of a VTR.
In the C1 series of the D-1 standard, as shown in FIG. 42, four correcting codes p, q, r and s are allotted to 60 data. In the C2 series, two correcting codes P and Q are allotted to 30 data. As shown in FIG. 43, in one track of the VTR, a plurality of data of FIG. 42 are continuously recorded. By the way, in one synchronous block, n (n .gtoreq.1) codes of the C1 series are provided.
Thus, in this example, the quantized output is classified in each frequency component by the conversion coefficient and the low frequency component is arranged in the reference position of each macro-block. Further, the macro-block pointer and the macro-block address showing the position on the picture are each arranged in synchronous block having an integral number of synchronous informations. By adding the code amount data L, the gross code amount of the macro-block can be caught and fixed in length within the frame. By the macro-block address and macro-block pointer, each macro-block and the position on the picture can correspond to each other.
However, if information such as the macro-block address, macro-block pointer or code amount data L is lacking, the decoding will not be able to proceed. For example, if an error is generated in the code amount data L, not only will that macro-block be erroneous but also the following macro-block, and will not be correctable until the macro-block address and macro-block pointer of the next synchronous block reach the designated part. Also, the respective macro-blocks are variable length coded and this a problem as special reproduction such as the quick feed reproduction of a VTR is impossible.